WO2015170276A1

WO2015170276A1 - Antenna array

Info

Publication number: WO2015170276A1
Application number: PCT/IB2015/053334
Authority: WO
Inventors: Derek Colin NITCH; Andries Petrus Cronje Fourie
Original assignee: Poynting Antennas (Pty) Limited
Priority date: 2014-05-09
Filing date: 2015-05-07
Publication date: 2015-11-12

Abstract

An antenna array (10) comprises a ground plane (12) and at least a first antenna array part (14). The first antenna array part comprises a first antenna (22) and a second antenna (24). Each of the first antenna and the second antenna is of generally truncated triangular shape and has a respective main axis (26) extending between a respective narrower end (30) and a respective wider end (34). The respective narrower ends are mutually facing one another and provide respective feed points for the first and second antennas. Each of the first antenna and the second antenna has a first part (40) diverging axially and linearly away from the ground plane in a direction from the narrower end towards an apex (38) and a second part (42) which extends in converging relationship with the ground plane from the apex in a direction away from the respective narrower end.

Description

ANTENNA ARRAY

INTRODUCTION AND BACKGROUND

This invention relates to an antenna array, more particularly a directional broad band dual polarized array.

With the long term evolution ("LTE") of networks such as 2G, 3G and 4G more sophisticated antenna arrangements are required to provide multiple input multiple output ("MIMO") and diversity support for the networks at customer premise equipment. The known antenna arrangements do not cover the bandwidth required whilst also providing two cables and associated ports each carrying a different polarization and/or are too complex and/or too large and/or too expensive.

Prior art arrangements comprise endfire log periodic structures sloping from their narrow (high frequency) end away from a ground plane in linear fashion. Such periodic structures have an active region which corresponds to the width of the structure and which in wavelength resonates at a specific frequency in that at high frequencies the narrowest part is active and at low frequencies, the widest part. By sloping linearly away from the ground plane, the height in terms of wavelength of the active region to the ground plane is constant giving a consistent main beam direction achieved including reflection from the ground plane. Often such a sloping log periodic structure is combined with a second and opposite endfire structure such that the respective narrow ends are closest to each other and the ground plane and the respective widest parts are furthest apart and highest from the ground plane. These structures then operate as a wide frequency band array where the spacing between active regions on either structure is constant (the same) in terms of wavelength and the height above the ground plane for both regions is also not changing in terms of wavelength even though both are increasing with decreasing frequency (increasing wavelength).

Although such arrays offer consistent pattern performance and other antenna parameters with changing frequency, they have the disadvantage that the height, width and length dimensions of an enclosure for the array are determined by the longest element (lowest frequency), since this element is the highest or furthest from the ground plane, is the widest and is furthest from the corresponding element on the opposite structure.

OBJECT OF THE INVENTION

Accordingly, it is an object of the present invention to provide an alternative antenna array with which the applicant believes the aforementioned disadvantages may at least be alleviated or which may provide a useful alternative array for the known arrays or arrangements. SUMMARY OF THE INVENTION

According to the invention there is provided an antenna array, the array comprising:

a ground plane; and

at least a first antenna array part comprising:

a first antenna and a second antenna;

each of the first antenna and the second antenna being of generally truncated triangular shape and having a respective main axis extending between a respective narrower end and a respective wider end;

the respective main axes being axially in line to form a main axis of the first antenna array part and the respective narrower ends mutually facing one another and providing respective feed points for the first and second antennas;

each of the first antenna and the second antenna having a first part diverging axially and linearly away from the ground plane in a direction from the narrower end towards a bend intermediate the narrower end and the wider end and a second part, which extends one of: a) parallel to the ground plane and b) in converging relationship with the ground plane from the bend in a direction away from the respective narrower end. In one preferred embodiment the bend forms an apex and the second part converges axially and linearly from the apex towards the ground plane in a direction away from the respective narrower end.

Each of the first antenna and the second antenna may be symmetrical about the respective antenna main axis.

Each of the first antenna and the second antenna may comprise a plurality (n) of discrete dipoles with a first and shortest dipole closest to the narrower end and the n^th and longest dipole closest to the wider end.

Each dipole may comprise respective first and second elements, have respective length dimensions and are arranged adjacent to and in spaced and parallel relation relative to one another.

At least some adjacent dipoles of at least one of the first and second antennas may be arranged with increased spacing relative to one another in a direction away from the respective narrower end.

The respective lengths of at least some dipoles of at least one of the first and second antennas may increase in a direction away from the respective narrower end. A width dimension of at least some of the dipoles of at least one of the first and second antennas may be proportional to the length dimension, that is, at least some of the longer dipoles may have a larger width dimension than the shorter dipoles.

The dipoles of at least one of the first and second antennas may be interconnected with a transmission line extending from the respective antenna feed point and linking the dipoles successively at respective dipole feed points with a signal phase reversal between the first and second elements at each successive dipole, as is well known in feeding log periodic dipole array antennas.

Each element may be of generally flat configuration having a length dimension and a width dimension. The elements may generally be of rectangular configuration. However, at least some of the longer elements towards the wider end of the antenna may increase in width in a direction away from the main axis of the antenna.

Each antenna may comprise first and second complementary structures which collectively form a transmission line feeding the first and second elements of each dipole of the antenna, out of phase.

The first structure may comprise a first elongate axial limb and may provide on one side of the first limb the first element of the first dipole and alternate dipoles of said plurality of dipoles and on another side of the first limb the second element of the second dipole and alternate dipoles of the plurality of dipoles.

The second structure may comprise a second elongate axial limb and may provide on one side of the second limb the first element of the second dipole and of alternate dipoles of the plurality of dipoles and on the other side of the second limb the second element of the first dipole and alternate dipoles of the plurality of dipoles.

The first and second structures may be superimposed on one another so that they collectively form one of said first and second antennas. The first and second limbs may be connected to one another at the ends thereof remote from the narrower end of the antenna.

The antenna may be associated with a frequency band extending from a lower frequency or longer wavelength associated with the n^th dipole and a higher frequency or shorter wavelength associated with the first dipole and the apex may be further than 0.15λ away from the ground plane, wherein λ is the wavelength of signals associated with a dipole of said plurality of diploes closest to the apex. The first and second structures may respectively be stamped from a conductive material or may comprise conductive tracks on a substrate, such as a printed circuit board (PCB).

The feed points of the first and second antennas may be connected to one another by a conductive bridge in the form of a transmission line. The bridge may be connected to a first cable and connector.

The array may comprise at least a second array part which is similar to the first array part and which is mounted with its respective main axis at an angle a relative to the main axes of the first array part.

The angle a may be any suitable angle, but is preferably 90 degrees. The feed points of the second array part may similarly be connected to a second cable and connector, so that the first and second array parts may be fed separately and with different polarities.

The antenna array is reciprocal in use in that it can be used either as a transmitting antenna or a receiving antenna or as both.

BRIEF DESCRIPTION OF THE ACCOMPANYING DIAGRAMS

The invention will now further be described, by way of example only, with reference to the accompanying diagrams wherein:

figure 1 is a perspective view of an antenna array; figure 2 is a section on line II in figure 1 ;

figure 3 is an exploded perspective view of a first antenna array part of the array in figures 1 and 2;

figure 4 is a perspective view of the first antenna array part of figure 3 in assembled form; and

figure 5 is a perspective view in more detail of a first antenna of the first antenna array part of figures 1 to 4, which antenna is rotated through 180 degrees

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

An antenna array is generally designated by the reference numeral 10 in figures 1 and 2.

The antenna array 10 comprises a conductive ground plane 12. Above the ground plane there is mounted as least one antenna array part 14. In figures 1 and 2, a preferred example embodiment comprising a first array part 4 and a second array part 16 is shown. The array parts are mounted with their respective main axes 18 and 20 at an angle a relative to one another and in the preferred embodiment, the angle a is 90 degrees. The array parts are identical in configuration and therefore, only first array part 4 will be described in more detail below.

First array part 14 is shown in more detail in figures 2 to 5 and comprises a first antenna 22 and a second antenna 24. Although the array part 14 in the example embodiment comprises dual log periodic dipole antennas (LPDA), any other logarithmic antenna may be used. Each of the first antenna and the second antenna are of generally truncated triangular shape and having a respective main axis 26 and 28 extending between a respective narrower end 30 and 32 and a respective wider end 34 and 36. The respective main axes 26 and 28 are axially in line to form the main axis 18 of the array part. The respective narrower ends 30 and 32 are mutually facing one another and provide respective feed points for the first and second antennas 22 and 24 which are connected via a first cable 33 (shown in figure 1 ) to a connector 35 for the first array part 14.

The first antenna 22 and the second antenna are similar in configuration and therefore antenna 22 only will be described in further detail below. Antenna 22 has a first part 40 diverging axially and linearly away from the ground plane 12 in a direction from the narrower end 30 towards a bend, in this example embodiment an apex 38, intermediate the narrower end 30 and the wider end 34 and a second part 42 converging axially and linearly from the apex 38 towards the ground plane 2 in a direction away from the narrower end 30 and towards the wider end 34.

In the example embodiment first antenna 22 is symmetrical about the main axis 26, which is best shown in figure 1. Further in the example embodiment, the first antenna 22 comprises a plurality (n) of discrete dipoles 22.1 to 22. n which are arranged in spaced and parallel relation and in increasing length from the narrower end 30 to the wider end 34 with a first and shortest of said dipoles 22.1 being adjacent the narrower end 30 and an n^th and longest of said dipoles 22. n being adjacent the wider end 34. Each dipole such as first dipole 22.1 comprises a first element 22.11 and a second element 22.12 and the n^th dipole comprises a first element 22. n1 and a second element 22. n2. In the example embodiment, each of said elements is of generally flat configuration and each dipole has a length dimension / and a width dimension w, which are indicated in figure 4 in respect of dipole 22. n. For at least some of the elements, the width dimension may be proportional to the length dimension, that is, at least some of the longer elements may have a larger width dimension than the shorter elements. The elements may generally be of rectangular configuration. However, at least some of the longer elements, such as elements 22. n1 and 22. n2 towards the wider end 34 of the first antenna 22 increase in width in a direction away from the main axis 26 of the antenna.

In the example embodiment and as best illustrated in figure 3, first antenna 22 comprises first structure 50 and second complementary structure 52 which collectively form a spine and transmission line for feeding the first and second elements of each dipole 22.1 to 22. n of the first antenna 22, out of phase.

The first structure 50 comprises a first elongate axial limb 54 and provides on one side A of the first limb 54 the first element 22.1 1 of the first dipole

22.1 and of alternate dipoles 22.3, 22.5,... etc of said plurality of dipoles and on another side B of the first limb 54 the second element 22.22 of the second dipole 22.2 and alternate dipoles 22.4, 22.6... etc of the plurality of dipoles. The second structure 52 comprises a second elongate axial limb 56 and provides on one side A of the second limb 56 the first element

22.21 of the second dipole 22.2 and of alternate dipoles 22.4, 22.6...etc of the plurality of dipoles and on the other side B of the second limb 56 the second element 22.12 of the first dipole 22.1 and alternate dipoles 22.3, 22.5... etc of the plurality of dipoles.

The first structure 50 and the second structure are superimposed on one another, so that they collectively form the first antenna 22. The first limb 54 and the second limb 56 are connected to one another at the ends thereof at the wider end 34 of the first antenna 22.

The first antenna 22 is associated with radio frequency signals having frequencies which fall in a frequency band extending from a lower frequency having a longer wavelength associated with the n^th dipole 22. n and a higher frequency f₂ having a shorter wavelength λ₂ associated with the first dipole 22.1 .

Referring to figure 5, the aforementioned apex 38 is at a height h further than 0.15λ away from the ground plane, wherein λ is the wavelength of signals associated with dipole 22.8, which is closest to the apex 38.

The first structure 50 and second structure 52 may respectively be stamped from a conductive material (as shown in figure 3) or may comprise conductive tracks on a substrate, such as a printed circuit board (PCB) (not shown).

The feed points at ends 30, 32 of the first and second antennas 22, 24 may be connected to one another by a conductive bridge 60 in the form of a transmission line. The bridge 60 and feed points are connected via first cable 33 to connector 35 as shown in figure 1.

Similarly, the bridge 62 and feed points at the corresponding ends of the antennae of second part 16 of the array 10 are connected via second cable 64 to connector 66.

As best shown in figures 2, 4 and 5, the structures 50 and 52 are supported above ground plane 12 by axially opposed insulating pedestals 70 and 72. The corresponding structures of second array part 16 are similarly supported.

The dimensions of the array are chosen such that each antenna array part provides a directional linearly polarized main beam perpendicular to the ground plane over a broad frequency band while reducing at least one of antenna height (maximum distance from the ground plane to the apex), antenna width and length. As illustrated above, the second antenna array part utilizes space not occupied by the first antenna array part and therefore provides a second polarization with substantially the same beam and bandwidth characteristics, whilst not increasing at least some of the dimensions of an enclosure which would be required to enclose the first antenna array part.

Hence each array part comprises a periodic endfire structure of which the first antenna part radiates towards the ground plane and in conjunction with reflections from the ground plane and the corresponding antenna part of the second antenna in the array part form a main beam perpendicular to the ground plane. The second part of the antenna radiates upwards (away from the ground plane). This wider part is too close to the ground plane (in terms of wavelength) to achieve effective reflection and at these frequencies, the proximity to the ground plane causes undesirable properties. By causing the wider parts to radiate upwards, these undesirable effects are reduced whilst also limiting at least overall antenna array height in comparison to the prior art configurations.

Claims

1. An antenna array, the array comprising:

a ground plane; and

at least a first antenna array part comprising:

a first antenna and a second antenna;

each of the first antenna and the second antenna having a first part diverging axially and linearly away from the ground plane in a direction from the narrower end towards a bend intermediate the narrower end and the wider end and a second part, which extends one of: a) parallel to the ground plane and b) in converging relationship with the ground plane from the bend in a direction away from the respective narrower end.

2. The antenna arrangement of claim 1 wherein the bend forms an apex and wherein the second part converges axially and linearly from the apex towards the ground plane in a direction away from the respective narrower end.

3. The antenna array according to any one of claims 1 and 2 wherein each of the first antenna and the second antenna is symmetrical about the respective antenna main axis.

4. The antenna array according to any one of claims 1 to 3 wherein each of the first antenna and the second antenna comprises a plurality (n) of discrete dipoles with a first dipole closest to the narrower end and the n^th dipole closest to the wider end, each dipole comprising respective first and second elements, have respective length dimensions and are arranged adjacent to and in spaced and parallel relation relative to one another.

5. The antenna array according to claim 4 wherein at least some adjacent dipoles of at least one of the first and second antennas are arranged with increased spacing relative to one another in a direction away from the respective narrower end.

6. The antenna array according to any one of claims 4 and 5 wherein the respective lengths of at least some dipoles of at least one of the first and second antennas increase in a direction away from the respective narrower end.

7. The antenna array according to any one of claims 4 to 6 wherein the dipoles of at least one of the first and second antennas are interconnected with a transmission line extending from the respective antenna feed point and linking the dipoles successively at respective dipole feed points with a signal phase reversal between the first and second elements at each successive dipole.

8. An antenna array according to any one of claims 4 to 7 wherein each antenna comprises first and second complementary structures which collectively form the transmission line and the dipoles.

9. The antenna array according to claim 8 wherein the first structure comprises a first elongate axial limb and provides on one side of the first limb the first element of the first dipole and alternate dipoles of said plurality of dipoles and on another side of the first limb the second element of the second dipole and alternate dipoles of the plurality of dipoles.

10. The antenna array according to claim 9 wherein the second structure comprises a second elongate axial limb and provides on one side of the second limb the first element of the second dipole and of alternate dipoles of the plurality of dipoles and on the other side of the second limb the second element of the first dipole and alternate dipoles of the plurality of dipoles.

1 1. The antenna array according to claim 10 wherein the first and second structures are superimposed on one another.

12. An antenna array according to any one of claims 4 to 11 wherein the antenna is associated with a frequency band extending from a lower frequency associated with the n^th dipole and a higher frequency associated with the first dipole, wherein the bend is further than 0.15λ away from the ground plane and wherein λ is the wavelength of signals associated with a dipole of said plurality of dipoles closest to the bend.

13. The antenna array according to any one of claims 9 to 12 wherein at least one of the first and second structures is stamped from a conductive material.

14. The antenna array according to any one of claims 1 to 13 comprising at least a second array part which is similar to the first array part and which is mounted with its respective main axis at an angle a relative to the main axis of the first array part. The antenna array according to claim 14 wherein the feed points of the first and second antennas of the first array part are connected to one another and to a first cable and connector and wherein the feed points of the first and second antennas of the second array part are connected to one another and to a second cable and connector.